Lava tubes Within the Zuni-Bandera Lava
Flows

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The following images were taken as part
of the 2000 Rockin' around New Mexico meeting, held in Grants,
New Mexico. The captions and locations were prepared by participants
on the field trip. For an enlarged version of any image, click
on the small version of the image.

Lava tubes are a very interesting feature
of basaltic lava flows. As basaltic lava cools, the outer part
can solidify to form a shell around the inner, still molten and
flowing part. The cool crust acts as a very effective insulator
for the inner, hotter lava, allowing it to flow for very great
distances, and greatly extends the distances over which basaltic
lava flows can travel. Single lava tubes up to 10 km in length
have been recognized in Hawaii (Francis, 1993). Lava tubes have
been recognized in many parts of the world, and also may have
been recognized on giant Martian volcanoes (Francis, 1993). The
following photos illustrate a number of features observed in a
lava tube called Junction Cave near Grants, NM.

GPS LOCATION: SE opening: N34° 58.142'
W108° 00.172'CAPTION:
This photo shows the collapsed entrance to a lava tube with people
decending. The entrance to the lava tube is probably similar
to the collapse pit seen
at the pahoehoe stop. The ground surface at the entrance appears
to be sandy with occasional large vesicular rock rubble. The
pahoehoe flow has been filled in by loess, wind deposition. The
tube that extends from the cave opening was formed by lava moving
at a moderate rate down a 1:3 to 1:5° slope over an extended
time. The tube is dendritic in shape, like a leaf, with small
side channels.

GPS LOCATION: NW opening: N34° 58.167'
W108° 00.229'CAPTION:
This photo shows the northwest opening of Junction lava tube,
looking from the northwest toward the main entry on the southeast
(where people are standing). This photo give an idea of the trend
of the lava tube. The two entrances are two collapsed portions
of the lava tube. Vegetation on the lava is rooted in several
inches of reddish sandy windblown dust, suggesting that the flow
is older than the McCarties flow. Plants include juniper, piñon
pine, ponderosa pine, Apache plume, rubber rabbit brush, Indian
paintbrush, prickly pear cactus as well as several grass species.

Lava at the surface is considerably weathered showing no volcanic
glass on its surface indicating a lava flow old enough for weathering
of the surface to have occurred.

GPS LOCATION: SE opening: N34° 55.142'
W108° 00.172' NW opening: N34° 58.167' W108° 00.029'CAPTION:
Keith Julian (2m tall) standing in front of large blocks of lava
in the Junction Lava tube. When the lava tube emptied, the lava
on the ceiling solidified and contracted upon cooling. This contraction
form fractures in the lava and large blocks subsequently fell
from the ceiling. If another lava flow had occurred through the
same tube, the new lava flow would have pushed these blocks along
with it, rounding the blocks into lava balls.

GPS: No locations could be taken in caveCAPTION:
"Looking Outward Toward Junction Cave Opening from the Inside".
The relatively small (2-meter high by 5-meter wide) opening to
this dendritic lava tube system is silhouetted against the dark
basaltic walls, roof, and floor of the Junction Cave. Note numerous
large blocks, which have dropped off the roof and now fill the
bottom of the cave interior, which might once have been more
than 10 meters high and 15 meters wide.

GPS: No locations could be taken in cave
CAPTION:
"Looking Inward into Junction Cave Lava Tube About 100 meters
from the Entrance:
Junction Cave is actually a complex dendritic lava tube system
more than 400 meters long, with several branching sub-tubes (hence
the designation "dendritic"). Among the unique features
formed naturally in large lava tubes found in the Malpais are:
"tube lining," which look like glazed elephant skin;
lateral "side benches" formed by multiple flows at
different levels; "curl-down" caused by highly plastic
cave wall lining breaking loose, with its top sagging inward;
and fallen "roof blocks" some of the size of refrigerators,
which have become unattached as a result of internal gravitational
mass wasting.

GPS: No locations could be taken in caveCAPTION: The side of the lava tube illustrates that pahoehoe
lava flows can be made up of many thin flows, rather than a single,
thick body. In this photo, it appears that at least 5 thin flows
are present, the breaks between flows being demarcated by the
presence of the vesicular (bubbly) horizons that form at the
top of a lava flow. Pahoehoe flows are not nececessily perfectly
flat, but can be lobate. A possible lobate flow tongue can be
seen half way up the right-hand side of the photo. To see an
active example of a lobate flow, click here.

GPS: No locations could be taken in caveCAPTION: This photograph also illustrates the presence
of multiple pahoehoe flows, but viewed from beneath, rather than
from the side. The vesicular top of the underlying flow can be
seen as the reddish areas on the photo. The overlying flow is
the blacker material. The overlying flow was apparently very
fluid when it was emplaced, because it conforms smoothly to the
top of the underlying flow.